1. Field of the Invention
This invention pertains to the fields of ordnance and ballistics. With greater particularity, this invention pertains to a gun barrel and projectiles or rocket assisted guided missiles for use therein. With greatest particularity, the present invention pertains to a gun barrel and projectile system wherein the performance advantages of a smooth bore barrel are achieved without compromising the ability to fire inexpensive spin stabilized rounds and while retaining the versatility to fire fin stabilized projectiles and gun launched rockets or guided missiles.
2. Description of the Related Art
Conventionally, gun barrels have been rifled by cutting a plurality of helical grooves defining lands therebetween in the bore. This is done for the purpose of engraving a projectile and causing it to rotate as it transits the barrel, thereby achieving spin stabilization of the projectile and increasing the accuracy and repeatability of its ballistic trajectory. One problem inherent in rifled barrels is that erosion of the rifling occurs at the muzzle, caused by the high velocity of the projectile and by muzzle efflux of hot propulsive gases, as the projectile exits the muzzle. This erosion rapidly reduces gun system projectile accuracy. A second problem with rifled barrels is that projectiles for use in rifled barrels must possess a sufficiently high level of structural strength, since little or no structural support is provided to the projectile by the barrel. This means that the set back forces in the projectile warhead, under very high acceleration, must be resisted by structure in the shell walls and the shell base.
As a consequence, only approximately ten percent of the projectile mass is high explosive or other warhead payload, the remaining ninety percent being inert structural mass. This same mass fraction limitation applies to gun launched rockets such as rocket assisted projectiles, where warhead mass fractions of only about ten percent are obtainable. For example, projectiles used in rifled gun barrels commonly will have a major diameter portion or bourrelet near the middle and perhaps a driving band at the rear which is in contact with the rifled bore surface. The frontal ogive portion and mid to rear portions of the projectile itself are often of smaller diameter than the gun barrel to avoid rifling wear as the shell expands under set-back pressure. This design requires the projectile to possess sufficient structural rigidity to resist deformation while undergoing the extreme acceleration environment of an artillery gun barrel during the firing sequence.
The muzzle velocity of rifled gun barrels is generally limited to between 3,000 to 4,000 feet per second. This is because rifling erosion which occurs at the muzzle is proportional to projectile muzzle velocity. Since, given equivalent ballistic coefficients, range is proportional to the square of the muzzle velocity, it can be seen that range is limited by muzzle velocity which in turn is limited by the amount of erosion which can be tolerated while still achieving the specified barrel life. Thus it may be seen that conventional rifled barrels firing conventional projectiles are limited in their performance by considerations of reasonable barrel life and the need to preserve accuracy of the ballistic trajectory, as well as structural requirements which greatly restrict the warhead payload capability.
These and other problems and limitations associated with the conventional rifled barrel and projectile have been overcome in the present invention which provides the accuracy advantages of a rifled barrel and spin stabilized or guided, rocket assisted projectiles without compromising the performance potential of a smooth bore barrel, in a versatile gun barrel and projectile system.